Slug-like creature pushes animal existence back 30 million years

Geologists from the University of Alberta have made a discovery that pushes the existence of animals back by 30
million years.

Life has been around on Earth for about 3.5 billion years, but
actual animals -- multicellular, eukaryotic
organisms -- are only half a billion years old. The oldest
confirmed animal was a slug-like organism called Kimberella,
dated at 555 million years old.

Now, that date has been pushed back. Alberta researchers found
fossilised tracks from centimetre-long, slug-like animal, which
were left in shallow-water sediment 585 million years ago.

The discovery was made in Uruguay by Ernesto Pecoits and Natalie
Aubet. They determined that the tracks were made by a primitive
animal called a bilaterian, and the soft-bodied animal's
musculature enabled it to move through the silt on the shallow
ocean floor.

There were no remains of the animal's body, just the tracks --
"generally when we find tracks of a soft-bodied animal, it's
usually just the body or just the tracks, not both," explains
Alberta paleontologist Murray Gingras.

How do you determine the age of a fossilized line in
shallow-water silt? We're glad you asked.

A team of geochronologists looked at particles of granitic rock
that were found invading the sandstone samples. Put those particles
through mass spectrometry equipment -- which bombards the sample with laser
beams -- and they can analysed and dated.

It took more than two years for the team to satisfy themselves
and a peer review panel of scientists that they had the right age
for the bilaterian fossils.